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Asters: How to Plant, Grow, and Care for Aster Flowers | The Old Farmer's Almanac

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Asters

Photo Credit
Pixabay
Botanical Name
Aster spp., Symphyotrichum spp.
Plant Type
Flower
Sun Exposure
Full Sun
Part Sun
Soil pH
Varies
Bloom Time
Summer
Fall
Flower Color
Blue
Pink
Purple
Red
White
Hardiness Zone
3
4
5
6
7
8
Special Features
Attracts Butterflies
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How to Plant, Grow, and Care for Aster Flowers

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Learn how and when to plant asters—daisy-like flowers that enliven the garden in early fall when many summer blooms are fading. These native perennials are deer-resistant and also provide late-season nectar for our pollinators!

About Asters

Asters are perennial flowers which bloom from late summer through fall. Growing 1 to 6 feet tall, depending on variety, these upright flowering plants bear cheerful star-shape flower heads that range in color from purple to white to blue.

Even though there are more than 600 aster species, the two most commonly encountered asters in the home gardening world are the New England aster (Symphyotrichum novae-angliae) and the New York aster (S. novi-belgii). Several years ago, the Aster genus was split into multiple genera. Aster now covers most European and Asian asters, while those native to North America now belong to Symphyotrichum.

A number of hybrid varieties are available in showy colors, yet “wild type” species native to your region are generally a wise choice for the ecologically-minded gardener, despite them not being quite as flashy as the cultivated varieties in some cases. Learn more about recommended varieties further down this page.

Aster is versatile: Depending on the height, it’s suitable for borders, rock gardens, or wildflower gardens. As well as being a valuable pollinator plant for bees and butterflies, its tasty seed heads are sought by cardinals, chickadees, finches, nuthatches, and many other seed eaters.

Planting

Asters prefer areas with cool, moist summers as well as cool nights, in sites with full to partial sun. In warmer climates, asters do not like the hot midday sun. Soil should be moist but well-drained, and loamy. Wet clay soil will lead to root rot and dry sandy soil will lead to plant wilt. Mix 2 to 3 inches of compost into the soil prior to planting. 

When to Plant Asters

  • The best time to put young aster plants in the ground is in mid- to late spring after danger of frost has passed. (See local frost dates.)
  • Or, you can plant mature, potted asters when they become available at garden centers (typically, in the late summer or early fall).
  • Asters can be grown from seed, but germination can be uneven. If desired, plant seeds in the fall or start them indoors in the winter. 

How to Plant Asters

  • When planting young aster plants outside in the spring, space them 1 to 3 feet apart, depending on the type and how large it’s expected to get.
  • Fully-grown asters, such as those available in late summer or early fall, should be planted about 3 feet apart.
  • If planting seeds, sow 1 inch deep in pots or flats and refrigerate them for 4 to 6 weeks to simulate winter dormancy. This cold period will kick-start germination.
  • Water well and spread mulch around the plants to keep the soil cool and prevent weeds.
Aster and monarch butterfly
Asters are highly attractive to pollinators, especially bees and butterflies.
Growing
  • Add a thin layer of compost (or a portion of balanced fertilizer) with a 2–inch layer of mulch around the plants every spring to encourage vigorous growth.
  • If  less than 1 inch of rain falls per week in summer, water regularly. But beware. Many asters are sensitive to too much or too little moisture. They will lose their lower foliage or not flower well. Watch for stress and try a different watering method if your plants are losing flowers.
  • Stake the tall varieties in order to keep them from falling over.
  • Pinch or cut back asters by one-third once or twice in the early summer to promote bushier growth and more blooms. Don’t worry, they can take it!
  • In winter, cut back asters after the foliage has died, or leave them through the winter to add some off-season interest to your garden. Birds may munch on the seeds, too.
    • Note: Aster flowers that are allowed to mature fully may reseed themselves. The resulting asters may not bloom true to their parent. (In other words, you may not get the same color flowers that you originally planted!)
  • Divide every 2 to 3 years in the spring to maintain your plant’s vigor and flower quality.
Recommended Varieties

The most common asters available in North America are the New England aster (Symphyotrichum novae-angliae) and the New York aster (Symphyotrichum novi-belgii). Both of these plants are native to North America and are great flowers for pollinators. We recommend planting a native species of aster over a non-native species when possible, so talk with your local Cooperative Extension or garden center about which species are best suited to your area. Look for varieties with disease resistance.

North American Asters

  • New England asters (S. novae-angliae): Varieties have a range of flower colors, from magenta to deep purple. They typically grow larger than New York asters, though some varieties are on the smaller side.
  • New York asters (S. novi-belgii): There are many, many varieties of New York asters available. Their flowers range from bright pink to bluish-purple and may be double, semi-double, or single.
  • Blue wood aster (S. cordifolium): Bushy with small, blue-to-white flowers.
  • Heath aster (S. ericoides): A low-growing ground cover (similar to creeping phlox) with small, white flowers.
  • Smooth aster (S. laeve): A tall, upright aster with small, lavender flowers.
  • Aromatic aster (S. oblongifolium): Multi-branched at base, stiff upright stems, with lavender or pink flowers.

European/Eurasian Asters

  • Frikart’s aster (Aster x frikartii) ‘Mönch’: Hailing from Switzerland, this mid-sized aster has large, lilac-blue flowers.
  • Rhone aster (A. sedifolius) ‘Nanus’: This aster is known for its small, star-shaped, lilac-blue flowers and compact growth.
Harvesting

Cut asters for flower arrangements when blooms are just beginning to open. Vase life is 5 to 10 days.

Asters have side shoots, which will continue to develop. These can be cut for indoor arrangements once they are the size you like.

Learn more about keeping cut flowers fresh.

Wit and Wisdom
  • The name “aster” comes from the Ancient Greek word for “star”—a reference to the plant’s star-shaped flowers.
  • Asters are called “Michaelmas daisies” because they bloom around September 29, which is the ancient feast day of St. Michael and a “quarter day,” marking the transition to autumn.
  • Asters, one of September’s birth flowers, were once burned to ward off serpents.
Pests/Diseases

Diseases: aster yellows; Botrytis blight; leaf spot, fungal; powdery mildew; rust; rot, Rhizoctonia root and stem, white smut, Fusarium wilt, Verticillium wilt.
Pests: aphids, foliar nematodes, slugs and snails, Tarsonemid mites.

Flowers
Perennials

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Comments

ErmaBlack (not verified)

2 months 2 weeks ago

I have a beautiful very large purple aster they I would like to split up and replant this fall is that a good idea.?

It’s best to divide flowering plants when they are not blooming. Because asters bloom so late into the year, it’s usually best to wait until early spring to divide and transplant them (chrysanthemums, too).

ErmaBlack (not verified)

2 months 2 weeks ago

May I split up a very large aster plant in the fall

Ci mcdonald (not verified)

1 year 3 months ago

Can they take heavy humid hot days of our summers??

Steve Morgan (not verified)

2 years 3 months ago

I had planted some Aster Flowers, this fall, so that I start getting flowering from the starting summer, few of them started drying up. So I bought a net from Olmsted's Nursery to avoid excess sunlight. Now they are doing well. Thank You!